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Updated: Nov 4, 2025

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Facile Access to Alkylideneborane and Diborabutadiene N-Heterocyclic Carbene Complexes
Hao Gao1, Qianli Li2, Ping Cui1
1School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, P. R. China.
Abstract:
A facile route to synthesis of B═C double-bonded systems has been developed. Specifically, both dibromofluorenylborane (FluH-BBr2) and a 1,1-dibromo-2,2-difluorenyldiborane/dimethyl sulfide adduct [(FluH)2B-BBr2(SMe2)] could be smoothly dehydrobrominated and subsequently coordinated by N-heterocyclic carbenes (NHCs) with formation of the respective alkylideneborane 1 and diborabutadiene 3. The electronic structures of 1 and 3 are interrogated and compared with those of base-free counterparts through density functional theory calculations.
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Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.